It is known to provide an arrangement in which video or television images of a sporting event are embellished by displaying computer generated images within the video images so that for example, these are superimposed on a field of play. For example, advertisements or club emblems of teams which are playing each other in a football match, for example, can be superimposed on an image of the football pitch which is captured by a camera, so that it appears that the players are playing on top of the images of the emblems which are superimposed on the football pitch. In order to achieve an effect wherein a computer generated image is superimposed on an image of a particular sports field, it is known to calibrate an image produced by the camera with respect to a model representing that image.
The term model as used herein will be used to designate a simulated representation of an object, which has a planar surface, such as a field of play from which images of that field of play are to be captured using a camera.
As disclosed in an article entitled “Flexible Calibration by Viewing a Plane from Unknown Orientations” by Zhengyou Zhang published in 1999 in ICCV, volume1, page 666, there is disclosed a method of self-calibration in which, a camera is moved in a static scene, and a rigidity of the scene provides two constraints on the camera's internal parameters from one camera displacement by using image information alone. The self-calibration is in contrast to photo-grammetric calibration in which a calibration object whose geometry in 3-D space is known with very good precision. The article discloses an arrangement for translating points within a model and points within the image so that points within the model can be mapped to the image and vice versa. However, the disclosed technique requires that a pattern be attached to planar surface of the image, which is captured before an estimation of five intrinsic parameters can be generated in order to translate between the model and the image.
Improvements in or relating to a process in which features or effects within a model can be represented within an image in a plane of a field of view such as a sporting field of play represent a technical problem particularly, for example when the translation is performed in real time.